The technique disclosed relates to backlight panel circuit, backlight panel and light emitting diode (LED) driver.
At present, Liquid Crystal Display (LCD) displays color images by operating the backlight panel which illuminates white light. The white light of the backlight panel is emitted from Light Emitting Diode (LED). As shown in FIG. 1, the backlight panel comprises a plurality of LED chains 12 each of which is consisted of LEDs 11, and LED driver 13 which causes the LED chains 12 to emit light. Each of the LED chains 12 comprises the same number of LEDs which are connected in series. The LED driver 13 supplies a voltage to each of the LED chains 12 so as to ensure the LEDs 11 on each of the LED chains 12 to emit normally.
The internal structure of the LED driver 13 in the prior art is shown in FIG. 2, which comprises a plurality of voltage followers (OP-AMP) 21, each OP-AMP 21 corresponding to a LED chain 12. The LED driver supplies a voltage to the LED chains through the output terminals of the OP-AMP 21. For example, a LED requires a voltage of 3V, and if there are ten LEDs of the same in one LED chain, a voltage of 30V is needed for the LED chain to emit normally. When the LED driver supplies voltage to the LED chains, the OP-AMPs function as voltage buffers and output the buffered voltages to the LED chains corresponding thereto in a one-to-one relationship. Assuming a liquid crystal panel of 20 inches, it needs one hundred of LEDs, and if one LED chain includes ten LEDs, there should be ten OP-AMPs in the LED driver, which will increase the cost of the liquid crystal panel.
In the prior art, a Pulse Width Modulation (PWM) signal transmitter transmits PWM signals to OP-AMPs in a predetermined PWM signal transmission cycle, which are used for controlling the OP-AMPs to output or not to output currents to the LED chains. The intensity of a light emitted by a LED chain depends on the average current intensity on the LED chain, which is a product of a current value of the current output from an OP-AMP to the LED chain and a duty ratio. The duty ratio is a ratio of an emission period of the LED chain to the PWM signal transmission cycle. For example, if the predetermined PWM signal transmission cycle is ten minutes and the actual emission period of the LED chain is two minutes, the duty ratio of the LED chain is 20%.
The present inventor found that there are a plurality of LED chains in a backlight panel and each chain needs to be connected to one OP-AMP. Thus, when there are too many LED chains in the backlight panel, the number of the OP-AMP being required is very large. In this case, the cost of the LED driver is increased much more, and since the LED driver is included in a liquid crystal display, the cost of the liquid crystal display also increases.